The present invention relates to a process, an apparatus and a tool for cutting a tubular bar.
In particular the present invention relates to the cutting of tubes made of plastic to which specific reference is made below, without thereby losing its general nature. In the technical sector concerning in particular the manufacture of tubes made of plastic it is known to perform cutting of the tube into segments of predetermined length by means of an apparatus of the type comprising a support frame on which there is mounted a drum rotatable about a horizontal axis coinciding with the axis of the tube to be cut. The drum has centrally a hole so as to be passed through coaxially by the tube to be cut, and supports, on a rotating surface arranged transversely with respect to the axis, a cutting arm having mounted on its end a circular cutting blade which operates around the tube itself
Apparatuses of this type may be used effectively also for the cutting of plastic tubes which are manufactured by means of continuous extrusion and, as such, have a continuous progression, extending along their longitudinal axis. In this case, the aforementioned frame is actuated by a movable carriage which is guided along the extrusion axis and moved by means of pneumatic/electric systems which effect the displacements thereof in phase with extrusion and the execution of each cut. These cutting apparatuses, although efficient and precise, also involve, however, some drawbacks arising from the fact that, during cutting of the entire thickness of the tubes, a portion, albeit small, of the shavings produced by the blade teeth is not conveyed towards the outside of the tube by the teeth of the blade itself and penetrates inside the tube, despite the fact that the apparatus is also provided with a cowling for removal of the shavings, which is associated with the blade and connected to a motor-driven aspirator for removing the shavings from the cutting zone.
With regard to the formation of plastic tubes, it is known that they normally have a cylindrical part and a flared or "belled" part, obtained with the aid of belling blocks which operate on the inside of the tube on the material thermoplastically heated in special ovens. If, inside the tube, shavings should be present in the portion of the tube intended to enter the heating oven, said shavings, during the time spent inside in the oven, tend to burn, with the emission of toxic gases.
If, on the other hand, the shavings contained in the tube should not enter inside the oven, but remain attached to the inner wall of the tube, during forming with the block the latter would crush them against the inner wall of the belling, preventing correct use thereof.
If, finally, shavings should be present in a more internal zone of the belling not affected by the aforementioned operations, the shavings could however cause blockage of the tube control members (taps, gate valves) if the tube were to be used for example as a conduit.
Finally, it must be mentioned that cutting devices which use circular cutting blades are somewhat noisy.